Teaching With Model Organisms

Model organisms are those that useful data sets have been already gathered to describe basic biological processes. And they are more amenable to asking certain questions due to their simplicity of structure and features (Bolker, 1995). In order to explore the advantages of using model organisms in classrooms, I will examine their desirable attributes, why certain organisms have been chosen as model organisms for teaching, the advantages of using model organisms in teaching, and examples of model organisms popular in biology instruction.

Characteristics of Model Organisms for Research and Instruction

A model system is a simpler, idealized system that can be accessible and easily manipulated (Rosenblueth & Wiener, 1945). Therefore, when selecting living organisms as models to work with, certain criteria are used depending upon the experimental purposes. As a result, there is a wide range of characteristics common to model organisms, including: 1) rapid development with short life cycles, 2) small adult size, 3) ready availability, and 4) tractability (Bolker, 1995). Being small, growing rapidly and being readily available are crucial in terms of housing them, given the budget and space limitations of research and teaching laboratories. Tractability relates to the ease with which they can be manipulated. For example, C. elegans is a popular research organism as it possesses all the characteristics mentioned, yet shares many essential biological properties with humans. For instance, researchers who study apoptosis (programmed cell death) use C. elegans as an experimental organism in the hope of finding treatments for certain types of human cancers, such as leukemia. By studying apoptosis in C. elegans, researchers hope to identify genes that switch-on cell death in cancer cells, thus, using the cell's own genetic machinery to rid the body of malignant cells. Because leukemia is the unregulated growth of white blood cells, identifying genes involved in apoptosis may provide researchers with a tool for treating the rapid proliferation of cancer cells.

Advantages of Using Model Organisms in Teaching Biology

Model organisms have long been used in the classroom to help students learn important concepts in various disciplines. Each discipline has its own set of organisms which have proven to be most suitable to use. For example, E. coli and Drosophila have been widely used as model organisms in introductory biology courses to teach microbiology and genetics.

There are three obvious advantages to using model organisms in teaching biology. First of all, in a laboratory setting, the model organism's immediate response to the change of environment will enhance students' learning and serve to hold their attention and interest. Furthermore, students not only understand what they see, but also believe it is real (Manney & Manney, 1992). Secondly, the use of model organisms involves hands-on activities that provide a unique experience that could not be obtained with other teaching methods (Rowan, 1981). Thirdly, by working with model organisms, students are able to explore scientific methods and concepts themselves. Moreover, they will come to understand about the investigative nature of the scientific enterprise, including how conclusions are drawn from data (Manney & Manney, 1992; Mertens, 1983). These three advantages might be obtained by using any living organism. However, model organisms are well-established experimental systems possessing certain properties, and are more amenable to classroom use (Bolker, 1995; Brenner, 1974).

Why Have Certain Living Organisms Been Chosen as Model Organisms in Teaching?

In general, scientists have to work with organisms different from the ones they wish to apply their findings to for several reasons (Bolker, 1995; Flannery, 1997). Krogh (1929) wrote " … for a large number of problems there will be some animal of choice or a few such animals on which it can be most conveniently studied." Model organisms act as surrogates that enable experiments to be carried out under a more favorable environment than would be available in the original system (Rosenblueth & Wiener, 1945).

The biological insights gained from using model organisms have helped to cure human diseases and improve people's understanding of life. Moreover, by studying organisms unrelated to humans, insight into scientific concepts can sometimes be more easily achieved. Paul Williams once mentioned that "Major advances in biology often come when diverse disciplines focus on model organisms." (Wisconsin Fast Plants (WFP), 2003). One example was the discovery of giant chromosomes in Drosophila's salivary glands that improved researchers' understanding of genetics.

The characteristics of model organisms that have made them useful in research laboratories also make them well-suited to classrooms (Manney & Manney, 1992). Compared to general living organisms, model organisms are well-established experimental systems and are often ready to be used in classrooms. The available resources, such as experimental protocols, for these model organisms make the transition of their use to curricula relatively simple. Thus, many are amenable to be used as experimental organisms in teaching.

Examples of Model Organisms Popular in Classroom Use

As discussed above, model organisms do play an important role in conveying biological concepts. Many model organisms have been used in the classroom. The fruit fly, Drosophila melanogaster, is the most obvious organism used in teaching. It is often used for students to learn Mendelian genetics. E. coli, yeast, and Rana pipiens are also popular model organisms in biology education. Within the past two decades, due to its importance and popular use in research, C. elegans has begun to take its place in the classroom as an important model organism. Below, I describe some of the model organisms, and the reasons that make them popular for classroom use.

Escherichia coli

Escherichia coli, a prokaryotic organism without a nuclear membrane, is a representative living material often used in laboratories and classrooms (Flannery, 1997). E. coli reproduces rapidly (under optimal situation 0.5 hr/generation) such that results for a number of experiments can be quickly obtained. Certain mutants of E. coli have been defined that cannot express certain proteins at saturation growth, and, therefore, die. E. coli was also the organism used to elucidate the regulation of the lac operon in genetics. E. coli's ability to take up exogenous genetic material under the procedure known as DNA-mediated cell transformation has also made it a popular model for studies using recombinant DNA (Moss, 1991). Using recombinant DNA techniques, E. coli can be manipulated in research laboratories and in the classroom to produce any DNA, RNA or protein of interest. Also, it is easy to manipulate both genetically and biochemically. Most importantly, it shares fundamental characteristics, such as DNA and messenger RNA, with all other organisms (Botstein & Fink, 1988). The value of E. coli in recombinant DNA makes it a good model organism for students to study the genetic material.

Drosophila

The fruit fly, Drosophila melanogaster, has been the most popular eukaryotic organism used in classrooms. It has been used in heredity and biomedical research where the aims are to understand human genetics and developmental processes. It is also a popular model for teaching Mendelian genetics. Drosophila is very popular and successful as a model organism because it has short life cycle of two weeks, making it possible to study numerous generations in an academic year (Flannery, 1997; Kramer, 1986; Sofer & Tompkins, 1994). It is easy to culture and inexpensive to house large numbers (Flannery, 1997; Jeszenszky, 1997; Kramer, 1986). Its size is amenable for cultivation in school laboratories. Also, it is large enough that many attributes can be seen with the naked eye or under low-power magnification (Sofer & Tompkins, 1994). Moreover, it has a very long history in biological research (since the early 1900s) and there are many useful tools to facilitate genetic study. For example, the use of antibodies makes the scoring of specific cells or cell types possible in Drosophila (Rubin, 1988; Sofer & Tompkins, 1994).

Because of the above properties, Drosophila has been used in research and teaching in a great variety of disciplines, such as classical and molecular genetics. Some researchers use Drosophila to study how its body plan is controlled by a set of homeotic genes. The more research is done using Drosophila, the better we understand it, thus making it an attractive model organism for class use (Flannery, 1997; Rubin, 1988).

Wisconsin Fast Plants

Wisconsin Fast Plants (WFP), mainly rapid-cycling Brassica rapa (B. rapa), were developed by Dr. Paul Williams at the University of Wisconsin - Madison, using classical selective breeding. The WFP, as well as Chinese cabbage and radish, belong to the Brassica genus, which is part of the Crucifer as family. The selection of fast growing Creicifers was desirable to speed-up plant biological research as traditional breeding of Brassica takes about six months. WFP has been used in the laboratory and classroom for studying basic and applied plant biology. For example, WFP can be used to study environmental science for students to see how pollutants affect living organisms, plant responses such as phototropic and geotropic responses, cell biology and other biology issues. The advantages of using WFP is that under continuous fluorescent light, they have a short life cycle (35 - 40 days). Compared to normal B. rapa, which produces at most two generations per year, one can harvest about ten generations per year from WFP. They are small (15 cm high, in a 2 cm2 pot) and can be housed in high densities and large numbers which make them especially good for school use. They are low-cost and easy to manage. They possess a wide variety of easily recognized traits that can be used in genetic studies. For instance, by crossing plants with light or dark plant colors, students can experiment on simple Mendelian genetics (WFP, 2003).

Caenorhabditis elegans

In the last two decades, a nematode, Caenorhabditis elegans, has captured the hearts of developmental biologists and geneticists hoping to solve the enigma of cell development and related biological problems, such as aging. In addition, educators have begun to use it in classrooms to illustrate central biological concepts, such as cell division (see "A Survey of Currently Used C. elegans Curricula"). Its popularity as a model organism is because it is transparent, thus cells of interest can be observed using a dissecting microscope. It is small (about 1- 1.5 mm) and easy to cultivate, which makes it possible to house large numbers of C. elegans. It has a short life cycle (3 days), which makes the production of numerous generations possible. It can be crossed at will. Male and hermaphrodites are the two sexes. Hermaphrodites can self fertilize or mate with males to produce offspring. Thus, cross or self-fertilization can be manipulated as desired. There are numerous tools available to study C. elegans, including different types of antibodies and advanced microscopes. Its genome has been completely sequenced. This is quite attractive and useful in genetic studies allowing researchers to pick a gene of interest to study (Donald, 1997; Wood, 1988). In sum, as discussed, some organisms are easy and amenable for use in the laboratory and the classroom to enhance our understanding of human biology. They are called "model organisms". A model organism is one that possesses the virtues of tractability and accessibility that can be used in experimental manipulation both in school and research.

Random Worm Term

The eukaryotic organelle containing DNA together with transcriptional machinery. DNA is organized into chromosomes. Prior to cell division chromosomes are replicated and then condense, at which time the nuclear membrane breaks down.